Lake Tahoe’s water level dropped to a four-year low on Tuesday as gusty winds and the impacts of California’s devastating drought hit the popular tourist destination.
After days of high winds increased evaporation rates, water levels fell to the basin’s natural rim for the first time since 2017, the end of the state’s last drought. The lake normally sits above the rim, which allows for water to flow into the Truckee River. Levels will probably continue to drop, receding below the rim this week, sooner than expected.
Though the lake’s water levels have fallen to this point several times in recent years, this week’s drop concerns researchers like Geoffrey Schladow, the director of the UC Davis Tahoe Environmental Research Center.
“It’s a sign of change at the lake,” Schladow said. “Change is very difficult to manage … When we start seeing things we’ve never experienced before at a greater frequency, it’s challenging.”
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Officials reported earlier this year that Lake Tahoe was experiencing its third-driest year since 1910. Between June 2020 and June 2021, the lake dropped about 3ft.
Once the lake falls below its natural rim, it will stop flowing into the Truckee River, cutting off a major source of water to the river, and the region will see more algae washing up on beaches. Winter weather will ultimately determine how long the low water levels will last, and the extent of the impacts in the region. Though snow has fallen in the area in the last month, water levels could fall below the rim again by next summer with even an average year of precipitation, Schladow said.
“To me the big danger is next summer,” he said.
Declining lake levels are already affecting the shoreline, drying up coves and boat ramps and forcing tour boat operators to find new ways to get customers on to the water, the San Francisco Chronicle reported.
“You can’t get within 150 yards of the normal shoreline” in South Lake Tahoe, Kelsey Weist, the owner of Clearly Tahoe, which runs tours around the lake, told the newspaper.
The entire region is grappling with impacts of the drought and the climate crisis. The US Forest Service cancelled Lake Tahoe’s annual fall salmon festival because low water levels meant Kokanee salmon would not spawn in nearby Taylor Creek.
Lake Tahoe saw unusually high water temperatures over the summer, a worrying development as warmer water makes the lake more hospitable to invasive species.
Meanwhile, the Caldor fire imperiled the region, forcing mass evacuations, upending the tourism industry and showering the area – and the lake – in thick ash. Smoke from the fire cooled the water temperature and reduced clarity in the lake, and researchers are still evaluating its impact.
Impacts of the alarmingly low level at Lake Tahoe
This week, a historically dry period in California will come to bear at Lake Tahoe, where the water level is expected to sink below the basin’s natural rim. That’s the point at which the lake pours into its only outflow, the Truckee River.
It’s not a crisis, researchers and conservationists say, but it marks another extreme swing for Tahoe amid historic drought, wildfires and erratic weather, all intertwined with climate change and becoming more prominent aspects of the alpine environment.
“Going below the natural rim won’t change much in the lake itself. But there’s very little positive about low lake levels once they get below the rim,” said Geoffrey Schladow, director of the Tahoe Environmental Research Center at UC Davis.
Tahoe’s natural rim rests at 6,223 feet in elevation. A dam on the Truckee River allows the lake to fill about 6 feet higher, to 6,229.1 feet, according to the U.S. Geological Survey.
The water level has fallen below the rim four times since 2004, most recently in the fall of 2016, the height of California’s historic drought. However, that tense period was followed by a banner winter for precipitation in the Tahoe area, in 2017, which replenished the Sierra snowpack and brought the lake to its highest heights in decades.
The water level has mostly been falling since the summer of 2019, when it was near the lake’s limit, and is currently about 1½ inches above the rim. The plunge is due primarily to meager snowpack in the mountains ringing the lake as well as evaporation, which sucks about 3 feet of depth off the lake each year, according to Tahoe water authorities.
This time, researchers and environmental nonprofits keeping watch of the lake aren’t optimistic about the water coming back as quickly as it did in 2017.
“If we have another dry winter, it could become a bigger concern,” Schladow said.
Tahoe has been steadily receding all year, and the plunging water level is changing the character of its shoreline.
The Truckee River, Tahoe’s only outflow, has slowed to a trickle. Private piers across the North Shore are high and dry. Boat ramps plunge straight into bare earth. Entire coves on the East Shore, popular with kayakers, have dried up. The South Shore has become one giant sandbar. Beaches in shallower areas have grown by hundreds of feet, exposing parts of the lake people aren’t used to seeing and revealing stinking deposits of rotting algae.
“You can’t get within 150 yards of the normal shoreline” in South Lake Tahoe, said Kelsey Weist, owner of Clearly Tahoe, which runs clear-bottom kayak tours around the lake.
The brunt of the impact so far has been felt by boating and tourism companies who have had to get creative about getting their customers on the water. Marinas are dredging more deeply to retain access for boaters.
Weist, who runs tours year-round, has adapted by overhauling her routes. A popular one that led paddlers along the Upper Truckee Marsh — typically a great place to spot wildlife — had to be canceled in early July, Weist said.
“We don’t foresee this being the last time we have this challenge,” Weist said.
No salmon anymore
Upper Truckee Marsh marks the spot where Tahoe’s largest inflow, the Upper Truckee, reaches the lake. It’s key habitat for kokanee salmon, which would normally be running upriver this time of year by the hundreds to spawn. But on Friday, under the afternoon sun, Jesse Patterson looked into the water there and counted only two. Nearby, piles of dead algae decayed on the beach.
“It’s crazy low,” said Patterson, chief strategy officer for the League to Save Lake Tahoe, a conservation and cleanup nonprofit. “The concern is what it looks like if this continues for multiple years in a row.”
Beyond cosmetics, there’s potential for environmental effects.
The lake water is warming, which has in turn given rise to algal blooms that have, in recent years, mucked up its famous clarity. The warmer the lake gets, the less likely it is to “turn over,” a periodic mixing phenomenon that helps keep the aquatic ecosystem balanced and healthy.
If water levels were to remain below the rim, Tahoe could become “terminal,” a designation of water bodies with no outflow. Those lakes come to be known for their high salinity and lack of aquatic life — the Salton Sea and Mono Lake are two examples in California.
Another possible change to Tahoe if water levels remain low: the emergence of the shallow sill at the mouth of Emerald Bay, which could separate the bay from the rest of the lake. Such separation “may occur at the mouths of many streams, cutting off access to spawning kokanee salmon next fall,” according to an email update from the Tahoe Environmental Research Center at UC Davis.
But there is reason for optimism: Snow has already fallen in Tahoe at least twice this month; a quarter-inch fell in parts of the lake on Monday.
“It is likely that winter will arrive in the next few months and the lake level will rise above the natural rim soon after,” according to the Tahoe Environmental Research Center. However, in its email, the center said that things could get worse.
“There is no limit to how many years drought conditions may persist and how low the water level may go. The most recent estimates suggest continuing drought conditions.”
What concerns lake advocates is the overall toll of more frequent extreme events — historic drought and low snowpack, high temperatures, smoky skies, the Caldor Fire.
And what about earthquakes?
We know seasonal effects can cause changes on faults, but what about less periodic climate phenomena, like a long-term drought? Might they cause changes too?
Lake Tahoe was swarmed by numerous earthquakes in May 2021 and April 2021. And many geologists feared the next ones could cause a massive tsunami (a bit like what has been proposed for the La Palma volcano):
As it turns out, changes in stress loads on Earth’s crust from periods of drought can, in fact, be significant. Research by JPL scientist Donald Argus and others in 2017 using data from a network of high-precision GPS stations in California, Oregon and Washington found that alternating periods of drought and heavy precipitation in the Sierra Nevada between 2011 and 2017 actually caused the mountain range to rise by nearly an inch and then fall by half that amount, as the mountain rocks lost water during the drought and then regained it. Such changes in stress loads on Earth’s crust could potentially be felt on faults in or near the range.
Similarly, pumping of groundwater from underground aquifers by humans, which is exacerbated during times of drought, has also been shown to impact patterns of stress loads by “unweighting” Earth’s crust.
Lundgren pointed to a 2014 study in the journal Nature by Amos et al. that looked at the effects of groundwater extraction in California’s Central Valley on seismicity on the adjacent San Andreas Fault.
The researchers found that such extractions can promote lateral changes in stress to the two sides of the San Andreas, which move horizontally against each other along the boundary of two major tectonic plates. This could potentially cause them to unclamp and slip, resulting in an earthquake.
“Such stresses are small, but if you have groundwater pumping over a long period of time, then they could become more significant,” he said. “Even though such changes might be small compared with stress changes caused by the normal buildup of stress on a fault from tectonic processes, it could potentially hasten the onset of the next big quake on the San Andreas. In addition, because the amount of slip on a fault increases with time between earthquakes, this could result in more frequent but smaller quakes.”
However, says Lundgren, the Fort Tejon segment of the San Andreas Fault that is nearest to the Central Valley last ruptured in 1857, so given the erratic nature of earthquakes along the fault and the great variability in time between events, with our current level of knowledge, scientists are far from understanding when and where the next large earthquake will occur on it.
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